Rate

Any

Regularity

Irregular pattern, but regular R-R

P waves

Upright and uniform

PRI

No relationship between P and QRS

QRS

May be narrow or wide

Rate

60-100

Regularity

Regular

P waves

Upright and uniform

PRI

0.12-0.20

QRS

0.08-0.12

Rate

60-100

Regularity

Slightly irregular

P waves

Bizarre/unusual

PRI

< 0.20

QRS

0.08-0.12